The long term goal of the proposed studies is to understand the mechanisms of cell signaling in the regulation of various cellular functions in different biological and disease processes. The previous funding period focused on the role of FIP200 (FAK- family Interacting Protein of 200 kDa) in the regulation of cell growth, proliferation, and apoptosis in breast cancer and embryonic development. We identified a novel interaction between FIP200 and TSC1 and showed that this interaction negatively regulates TSC1- TSC2 complex function to increase mTOR activation and cell growth. We also found that FIP200 inhibited cell cycle progression through its regulation of the cyclin dependent kinase inhibitor p21 and cyclin D1 in breast cancer cells. We generated FIP200 knockout (KO) mice and showed that deletion of FIP200 resulted in embryonic lethality associated with defective liver and cardiac developments, suggesting an essential role of FIP200 in embryogenesis. Consistent with studies in vitro, deletion of FIP200 led to an increased activity of TSC1-TSC2 complex and corresponding cell size decrease in the embryos. Analysis of FIP200 KO mice as well as isolated MEFs and hepatocytes also suggest a role for FIP200 in the regulation of cell survival and apoptosis. Further analysis showed that FIP200 is required for TNF1-induced JNK activation, and reduced JNK activation and its pro-survival function upon FIP200 deletion is responsible for the increased susceptibility to TNF1-induced apoptosis in FIP200 KO cells. In preliminary studies, we found a potentially important role of FIP200 in the central nervous system as neural specific FIP200 conditional KO in mice resulted in cerebellar degeneration and ataxia, which are associated with progressive loss of Purkinje cells, spongiosis and increased apoptosis in the cerebellum. We also found an abnormal accumulation of ubiquitinated protein aggregates, but no decrease in the proteasome activity in the FIP200 conditional KO mice. Additional studies with FIP200 KO MEFs suggested a role for FIP200 in autophagosome formation. Despite these progresses suggesting important functions of FIP200 in cerebellar degeneration and ataxia, little is known about the molecular and cellular mechanisms by which FIP200 regulation of signaling pathways and cellular processes in the neurodegenerative diseases. Based on our previous and preliminary studies, we propose to 1). Analyze molecular mechanism of FIP200 regulation of survival and axonal development of Purkinje cells using primary culture of isolated cerebellar neurons, 2). examine the role and mechanisms of FIP200 in cerebellum degeneration in vivo by using mouse genetic interaction approaches, and 3). study the cellular basis of FIP200 functions in cerebellum degeneration by creating and analyzing additional conditional knockout mice models in which FIP200 is deleted in cerebellum neurons other than Purkinje cells or just in Purkinje cell specifically. PUBLIC HEALTH RELEVANCE: Neurodegenerative diseases are major and increasing health threats as a result of the increased life expectancy and aging population in the United States. Elucidation of the roles and mechanisms of FIP200 in cerebellar degeneration in this proposal will not only advance our understanding of the mechanisms of signal transduction by FIP200 in vivo but also provide significant insights into molecular and cellular mechanisms of neurodegenerative disorders that may contribute to novel therapy for these devastating diseases.